All-optical wavelength conversion is an important feature of multi-wavelength optical systems such as wavelength-switching networks. Solutions to provide all-optical wavelength conversion have been studied to a great extent in the context of wavelength-switching, because they simplify network management, and provide superior blocking performance (see B. Ramamurthy and B. Mukherjee, “Wavelength-conversion in WDM networking”, IEEE Journal on Selected Areas on Communications, vol. 16, pages 1061–1073, September 1998). These solutions comprise hardware designs for elementary converters (see S. Yoo, “Wavelength-conversion technologies for WDM network applications”, IEEE Journal of Lightwave Technology, vol. 14, pages 955–966, June 1996; J. Elmirghani and H. Mouftah, “All-optical wavelength conversion: technologies and applications in DWDM networks”, IEEE Communications Magazine, pages 86–92, March 2000), as well as techniques to make the best use of limited wavelength conversion resources. Several hardware designs are possible for all-optical wavelength conversion, which include cross-gain or cross-phase modulation in semiconductor optical amplifiers, as well as wave-mixing techniques based on nonlinear media. The devices resulting from these different techniques have diverging characteristics in terms of their transparency, their bandwidth, and their bulk wavelength conversion capability. For example, devices based on cross-gain modulation provide limited signal transparency and have no bulk wavelength conversion ability, as they only accept one input signal at any time. On the other hand, these devices have a mature manufacturing process. They have been commercially available for several years. Wave-mixing converters are more recent but offer many advantages, such as a high signal transparency and bulk wavelength conversion capabilities. Yet their manufacturing processes are still immature. In general, all-optical wavelength converters remain expensive. Therefore, we need to minimize requirements for such devices in any multi-wavelength system.
The above mentioned evolution has constrained previous solutions to using converters with no bulk wavelength conversion capacity, like the ones based on cross-gain modulation. Converters with no bulk wavelength conversion capability, which are also called single-input converters, offer few options to provide wavelength conversions in multi-wavelength systems. The solutions are limited to mapping each input frequency to its image by an atomic wavelength conversion, which is implemented with dedicated converters. This technique enables the building of strictly non-blocking multi-wavelength optical cross-connects (see B. Ramamurthy et al. referenced above). However, it produces high converter costs, as the number of all-optical converters is O(F.W), where W is the number of wavelengths and F is the number of fibers.
The development of wave-mixing converters has motivated new techniques for wavelength conversion. Some of these solutions reduce converter requirements by exploiting bulk wavelength conversion inherent in wave-mixing (see N. Antoniades, S. Yoo, K. Bala, G. Ellinas, and T. Stern, “An architecture for a wavelength-interchanging cross-connect utilizing parametric wavelength-converters”, IEEE Journal of Lightwave Technology, vol. 17, pages 113–1125, July 1999). In such architectures, input frequencies are usually converted to their image, through a cascade of elementary wavelength conversions. These conversions follow parametric relationships characterizing the type of wave-mixing converter used (see S. Yoo referenced above). For example, in the case of converters based on difference-frequency generation, each input frequency f is mapped to fp−f, where fp is the pump frequency of the converter. For example, rearrangeable wavelength-interchanging cross-connects have been proposed that are based on a modified Benes interconnection topology (see N. Antoniades et al. referenced above). However, these techniques do not lead to any dramatic reduction of converter requirements. Indeed, the most efficient technique described so far still uses a number of wave-mixing converters, of the order of the number of wavelengths, per fiber (see N. Antoniades et al. referenced above). Most previous work focuses on the design of all-optical wavelength switches that have the capability to provide dynamic mappings between incoming wavelengths and outgoing wavelengths. Yet few studies consider the problem of the all-optical implementation of static frequency mappings. Such mappings have an important role in all-optical signal processing.
In view of the foregoing, it would be desirable to provide a technique for optically converting wavelengths in a multi-wavelength system in an efficient and cost effective manner which overcomes the above-described inadequacies and shortcomings.